This application is based on and incorporates herein by reference Japanese Patent Application No. 2000-18068 filed Jan. 25, 2000.
This invention relates to an activating device used for a vehicular passenger protection system such as an airbag system, belt pretensioner, or the like mounted on a vehicle.
Heretofore, for example, a mechanical switch has been employed as a switch for supplying an activating current to squib in an activating device of a vehicular airbag system. Because the mechanical switch is prevented from malfunction even though erroneous operation of a microcomputer mainly due to erroneous operation of a built-in CPU occurs, the mechanical switch has been employed as a safety switch for activating squib.
However, the mechanical switch is expensive and large-sized disadvantageously. Furthermore, because the closing retention time of the mechanical switch is short, the closing retention time required for the delayed control in which an airbag is started with retardation from the activating of a belt pretensioner or the retardation time between the first step and second step of a two-step activating airbag is controlled is not secured. As a result, the activating device is not sufficient in the passenger protection performance disadvantageously.
Therefore, recently there is increasing need for replacing a mechanical switch with an electronic switch in order to reduce the cost and in order to improve the passenger protection performance.
Generally, an activating device has the structure in which a plurality of electronic switching elements are connected to a squib in series in the case that a mechanical switch is replaced with an electronic switch. However, it is required for replacing a mechanical switch with an electronic switch that these plurality of electronic switching elements will not be erroneously turned on simultaneously due to erroneous operation of a microcomputer, that is, an airbag system is prevented from being erroneously activated.
Particularly, the close attention must be paid when one electronic switching element is turned on forcedly for failure diagnosis because redundancy of erroneous activating prevention is reduced.
It is an object of the present invention to provide an activating device used for a vehicular passenger protection system that prevents erroneous activation due to erroneous operation of a microcomputer.
According to the present invention, a plurality of electronic switching elements is connected in series each other with a squib to activate the squib when turned on. The electronic switching elements include a diagnosis target switching element and a non-diagnosis target switching element. First and second acceleration sensors detect acceleration of a vehicle, respectively. A first vehicle collision is determined based on at least a detection output of the first acceleration sensor, and a second vehicle collision is also determined separately by a microcomputer based on at least a detection output of the second acceleration sensor. The diagnosis target switching element is turned on based on at least the first vehicle collision determination, and remaining electronic switching elements are turned on based on at least the second vehicle collision determination. The diagnosis target switching element is forcedly turned on to be diagnosed with respect to its malfunction in response to a diagnosis signal produced from the microcomputer. The diagnosis target switching element and the non-diagnosis switching element are inhibited from being turned on concurrently regardless of an output condition of the microcomputer. Thus, the diagnosis target switching element is diagnosed only under a condition that the non-diagnosis target switching elements are being turned off.